This invention relates to the field of lubricious hydrophilic coatings for intracorporeal medical devices such as, for example, a catheter or guidewire.
The use of a medical devices within a patient may be facilitated by the presence of a lubricious surface on the device. For example, intravascular devices, such as catheters and guidewires, are more easily maneuvered within a patient's vasculature when the friction between the walls of the vessel and the intravascular device is reduced. The friction may be reduced by coating the device with a hydrophilic compound which becomes slippery after adsorbing an appreciable amount of water. Consequently, the hydrophilic coating provides lubricity when the coated device is exposed to aqueous solution, as when the coated device is exposed to water prior to insertion in the patient or to the patient's blood during use. Alternatively, coatings, such as fluoropolymers, and silicone, provide lubricity to the surface of an intracorporeal device without the need for exposure to aqueous solution. However, the degree of lubricity may vary greatly depending on the nature of the lubricious coating. Hydrophilic coatings provide superior lubricity compared to hydrophobic coatings, such as silicone, when tested against a biological tissue countersurface.
In addition to lowering the coefficient of friction of the coated device, an effective lubricious coating must strongly adhere to the device surface. The lubricious coating should remain adhered to the device surface during potentially extended periods of storage, as well as in response to abrasive forces encountered during use. Poor adhesive strength is undesirable because the lost coating may be left behind inside the patient during use, with a corresponding decrease in the lubricity of the device. Typically, a trade off exists between a coating's lubricity and the coating's adhesive and cohesive strength, so that attempts to increase the durability of lubricious coatings may inadvertently decrease the lubricity of the coating. Durability is particularly an issue on the surfaces of catheters and guidewires which are subjected to significant rubbing and abrasive forces as the devices are slidably advanced through the patient's tortuous vasculature. Consequently, one difficulty has been providing a highly lubricious coating with long lasting lubricity on a surface of a catheter or guidewire.
“Watermelon seeding” is a term known in the art to describe a phenonemon which can occur when the medical device is lubriciuosly coated. This term refers to slippage of the balloon wherein the balloon which is too lubricious and shoots forward upon inflation causing accidental slippage from the target or repair site which can ultimately may lead to stent slippage from the target site as well. This phenomenon has been addressed in the art by selectively coating the folded balloon so that when the balloon is being inflated, uncoated balloon sections decrease the slipperiness of the balloon surface.
In the case of a guidewire, it is advantageous to have an lubricious coating applied to the outer surface of the device as well since the coating helps to cross the often tight lesion. However, if the distal tip or distal section of the guidewire is too lubricious, there could be a loss of tactile feel to the interventional cardiologist. Still, it is desirable to have some lubricity at the distal end of the guidewire to maintain lesion crossability and control.
Therefore, it would be a significant advance to provide a highly durable hydrophilic coating on the outer surface of a medical device to render the device highly lubricious but which avoids “watermelon seeding” of the balloon catheter and the loss of tactile feel in the case of a guidewire. The present invention satisfies these and other needs.